DE 34 02 613 C1 discloses a length-measuring device of the above-mentioned type. The length-measuring device includes a hollow section member in which a scale extends in the longitudinal direction. During measurement operation, the scale is scanned by a scanning unit, which is attached to an object to be measured via a drive dog. The drive dog extends through a seal that seals an opening extending in the longitudinal direction of the hollow section member. The seal is attached to the hollow section member in such a manner that it is stretched in the longitudinal direction. Attachment of the seal is accomplished by clamping using a screw and a clamping plate.